The present invention relates generally to systems for recycling woodwaste, and more particularly, to an apparatus and method for separating contaminates from woodwaste to produce wood fuels and other usable products.
The forest products industry has been converting sawmill waste into a source of fuel for over a hundred years. According to current information, 80 percent of the total biomass residue converted to energy is derived from processing forest waste. Until recently, the term "biomass" referred to waste products of forest, agricultural, dairy, and animal products industries. With increased tipping fees at waste disposal sites (landfills) and a shortage of such sites in urban areas, there is an ever-increasing incentive to separate woodwaste from the urban waste stream, and to recycle it into a biomass boiler fuel and other usable products.
Based on recent data, 20 to 25 percent of all solid waste disposed of in urban areas is wood, or woody and fibrous organic material. This material is from discarded pallets, wood cratings, tree limbs, stumps, demolition waste, construction projects, and manufacturing industries. The vast majority of this material is transported to landfills for burial, adding to the nation's solid waste disposal crisis.
Burying woodwaste in landfills is not only a waste of a potential fuel, but is becoming an unmanageable problem in terms of finding adequate space for such landfills. It is difficult to document the amount of woodwaste being landfilled nationwide. However, in metropolitan New York alone, it is believed that about 10,000 tons per day are being landfilled. In addition to finding suitable landfill areas, landfilling is expensive, costing between $25.00 and $125.00 per ton. The environmental impact of landfilling is also just now being confronted through federal clean up and monitoring programs like the EPA Superfund. The simplest way to lessen the environmental impact is to decrease the amount of woodwaste going into landfills.
Of course, not all urban woodwaste can be economically separated from the waste stream, and some wood materials should not be utilized as fuel, as they may be contaminated with creosote, asbestos and/or formaldehyde. Even with these factors considered, recycling only 25 percent of the woodwaste that New York generates daily would provide 2,500 tons per day of biomass wood fuel. Providing a cost-effective way of separating this biomass fuel source from the waste stream should encourage the recycling of more woodwaste, decreasing the amount deposited in landfills and decreasing energy costs. The technology to utilize woodwaste as a fuel is existing and fully commercialized in many areas. Plants such as Gaylord Container Company of Antioch, Calif. have been supplementing their woodwaste fuel with recycled urban woodwaste since the early 1980's, producing steam and 28 megawatts of electricity. At the present, in California alone, for example, there are at least 17 different facilities generating 205 megawatts of electricity utilizing a small percentage of recycled urban woodwaste as fuel.
Various equipment is currently on the market for processing wood and yard waste debris. For example, one such piece of equipment, sold by the assignee of the present invention, and known as the W.H.O Wood Waste Tub Grinder, can process wood and yardwaste six feet long and up to twelve inches in diameter at a rate of 10 to 25 tons per hour. Private companies and municipal public work departments utilizes these grinders to recycle woodwaste and yardwaste into boiler fuel, landscaping products, soil amendments, and bulking agents.
However, there is a real need in the marketplace for equipment suited to screen and size woodwaste into a cleaner fuel. When marginal truckloads of wood fuel are turned away because the fuel does not meet the boiler plant's specifications, or a wood fuel supplier is restricted from processing available wood because of its dirt, metal, plastic, and/or yard waste content, the supplier's operating costs go up. Those costs must be covered, which, in turn, makes urban woodwaste less attractive as a fuel source. Additionally, higher operating costs limit others from entering the field. Contaminated (marginal) woodwaste can be processed only if the contaminates can be efficiently and economically removed. If the contaminants are removed, the processed product that is unsuitable for fuel may still be marketable as landscaping products.
Woodfueled biomass, electrical-generation facilities can burn fuel from in-forest residues, forest industry woodwaste and urban woodwaste. Of the three wood fuels, urban woodwaste rates the highest in BTU value and lowest in moisture content. Therefore, it burns at a higher efficiency than the other types of woodwastes. For instance, recycled urban wastewood has an energy content of 8,000 to 9,000 BTUs per pound and a moisture content of 10-15 percent (wet basis). Harvested wood chips (in-forest residues) are rated at 6,000 BTUs per pound with a moisture content of about 35 to 45 percent (wet basis), and forest industry wastewood is rated about 7,500 BTUs per pound with a moisture content of between about 10 and 30 percent (wet basis). Thus, wastewood from the urban stream has a 30 percent higher energy content than in-forest residues and a 15 percent higher energy content than forest industry waste. As such, the use of urban woodwaste can provide increased efficiencies in electrical energy generation plants burning such materials.
At present, it is thought that of the wood fuel types burned in boilers only about 3 percent is produced from urban woodwaste. If more of the higher BTU, urban woodwaste could meet wood fuel specifications, then the operating efficiencies and cost-effectiveness of these plants would improve. Thus, recycled urban woodwaste is the most valuable of any wood fuel product when it is screened of contaminates such as plastics, metals, dirt, and leaves as required by fuel buyers.
In addition to reducing the ever-increasing amounts of woodwaste that must be disposed of, recycling woodwaste into high-quality wood fuel should produce a decreased demand on non-renewable energy sources such as petrochemical products. The system of the present invention provides an economic and efficient way to tap an energy supply which has in the past been largely left untouched. It also provides an efficient way for producing marketable products other than fuel from contaminated woodwaste.
In view of the foregoing, it is an object of the present invention to provide a system capable of producing a less contaminated wood fuel from a wider source of woodwaste.
Another object of the present invention is to provide an economically-viable alternative to landfilling woodwastes.
Yet another object of the present invention is to provide high quality, marketable end products from urban woodwaste.